Function verify_served_key_package 

pub fn verify_served_key_package(
    crypto: &RustCrypto,
    id: &InstallationId,
    package: &KeyPackage,
) -> Option<Result<VerifiedKeyPackageV2, KeyPackageVerificationError>>

Verify the package served for id. A package whose leaf key is another installation’s was not served for id, so it is left out.